Design of a digital multiradian phase detector and its application in fusion plasma interferometry

Mlynek, A.; Schramm, G.; Eixenberger, H.; Sips, G.; McCormick, K.; Zilker, M.; Behler, K.; Eheberg, J.

doi:10.1063/1.3340944

Cited by 58 publications

(57 citation statements)

References 11 publications

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“…We show here in panel (a) the heating powers, in particular P NET , in box (b) the line integrated densities from the core and edge interferometry channels, whose geometry is given in [13]. In panel (c), the usual D α signal in the divertor allows identifying the L-H transition and the ELMs.…”

Section: L-h Transition and Elm Behaviourmentioning

confidence: 99%

L–H transition in the presence of magnetic perturbations in ASDEX Upgrade

et al. 2012

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Abstract.The L-H transition and the H-mode behaviour in the presence of non-axisymetric n=2 magnetic perturbations have been investigated. At low density no effect on the L-H transition is observed. Within a rather narrow density window around 50% of the Greenwald density limit, a transition to H-mode with small ELMs only and good confinement can be achieved. However, a strong density dependence of the L-H threshold power in the presence of magnetic perturbations forces the plasmas to remain in L-mode when the density is above 60% of the Greenwald value. The H-mode confinement time is not affected by the presence of the magnetic perturbations. All these H-modes, with and without ELM mitigation, exhibit a common confinement degradation with increasing recycling.

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Section: L-h Transition and Elm Behaviourmentioning

confidence: 99%

L–H transition in the presence of magnetic perturbations in ASDEX Upgrade

et al. 2012

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“…The alignment of the profiles is simultaneously performed with respect to the electron density, , profile as the TS system has identical measurement volumes for both and . The measurements from TS are complemented by those obtained with the lithium beam (LIB) diagnostic [33,34], which are shifted such that they match those of TS, and the interferometry system [35]. The latter is used to constrain the electron density at the pedestal top.…”

Section: Derivation Of From Cxrs Measurementsmentioning

confidence: 99%

High-accuracy characterization of the edge radial electric field at ASDEX Upgrade

et al. 2013

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Abstract. The installation of a new poloidal charge exchange recombination spectroscopy (CXRS) diagnostic at ASDEX Upgrade (AUG) has enabled the determination of the radial electric field, , using the radial force balance of impurity ions.has been derived from charge exchange (CX) spectra measured on different impurity species, such as He 2+ , B 5+ , C 6+ and Ne 10+ . The resulting profiles are found to be identical within the uncertainties regardless of the impurity species used, thus, demonstrating the validity of the diagnostic technique. The profile has been compared to the main ion pressure gradient term, which is found to be the dominant contribution at the plasma edge, thus, supporting that the well is created by the main ion species. The profile has been measured in different confinement regimes including L-, I-and H-mode. The depth of the well and the magnitude of the shear are correlated with the ion pressure at the pedestal top. The temporal evolution of the measured CX profiles and the resulting have been studied during an ELM cycle. At the ELM crash, the minimum is less deep resulting in a reduction of the E×B shear. Within 2 ms after the ELM crash, the edge kinetic profiles have nearly recovered and the well is observed to recover simultaneously. In high density type-I ELM mitigated H-mode plasmas, obtained via externally applied magnetic perturbations with toroidal mode number = 2, no clear effect on due to the magnetic perturbations has been observed.

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“…The strong transient local perturbation caused by the pellet has a serious impact on several diagnostics and AUG control systems, which required dedicated attention and action to Final version, 6.1.2012 counteract. The plasma density feedback control system, as well as the low-density interlock of the auxiliary heating systems required for machine protection, usually rely on the lineintegrated density measurement provided by the DCN laser interferometer [19]. Strong local density gradients occurring during pellet ablation, however, cause refraction of the laser beam and make this measurement unreliable due to occurrence of fringe jumps.…”

Section: Experimental Set-up and Status Of Coil And Pellet Systemmentioning

confidence: 99%

High-density H-mode operation by pellet injection and ELM mitigation with the new active in-vessel saddle coils in ASDEX Upgrade

et al. 2012

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Recent experiments at ASDEX Upgrade demonstrate the compatibility of ELM mitigation by magnetic perturbations with efficient particle fuelling by inboard pellet injection. ELM mitigation persists in a high density, high collisionality regime even with the strongest applied pellet perturbations. Pellets injected into mitigation phases trigger no type-I ELM like events unlike when launched into unmitigated type-I ELMy plasmas. Furthermore, the absence of ELMs results in improved fuelling efficiency and persistent density build up. Pellet injection is helpful to access the ELM-mitigation regime by raising the edge density beyond the required threshold level, mostly eliminating the need for strong gas puff. Finally, strong pellet fuelling can be applied to access high densities beyond the density limit encountered with pure gas puffing. Core densities of up to 1.6 times the Greenwald density have been reached while maintaining ELM mitigation. No upper density limit for the ELM-mitigated regime has been encountered so far; limitations were set solely by technical restrictions of the pellet launcher. Reliable and reproducible operation at line averaged densities from 0.75 up to 1.5 times the Greenwald density is demonstrated using pellets. However, in this density range there is no indication of the positive confinement dependence on density implied by the ITERH98P(y,2) scaling.Final version, 6.1.2012 2 IntroductionThe power load deposited by type-I ELMs onto the first wall and divertor presents a severe danger for ITER. Currently, there are several options for ELM mitigation: Operating with plasma scenarios which develop no or only benign ELMs, ELM pace-making to enhance the ELM frequency by at least a factor of 15 -30 in order to reduce individual ELM losses by this same factor, or ELM mitigation or ELM suppression with non-axisymmetric magnetic perturbations. Pace-making tries to reduce the type-I ELM size by triggering the instability through an external perturbation, e.g. pellet injection with a rate higher than the natural ELM frequency. Avoidance of type-I ELMs is preferred over ELM pace-making if it can be achieved without significant deleterious impact on the plasma performance. Nonaxisymmetric magnetic perturbations have been investigated in DIII-D where full suppression or at least significant mitigation of ELMs has been achieved over a wide operational range [1]. This successful first demonstration prompted further experiments at JET [2,3], NSTX [4] and MAST [5] with different perturbation field configurations. In theses experiments, quite different results with respect to ELM mitigation were obtained, and so far full ELM suppression has not been reproduced in any of them. Recently, the ASDEX Upgrade tokamak has been enhanced with a set of in-vessel coils [6] in order to study ELM amelioration, shed light on the physics involved, and to improve the extrapolation base for ITER. In a first stage of this enhancement, n=2 magnetic perturbations are found to allow suppressing type-I ELMs and replace th...

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Design of a digital multiradian phase detector and its application in fusion plasma interferometry

Cited by 58 publications

References 11 publications

L–H transition in the presence of magnetic perturbations in ASDEX Upgrade

L–H transition in the presence of magnetic perturbations in ASDEX Upgrade

High-accuracy characterization of the edge radial electric field at ASDEX Upgrade

High-density H-mode operation by pellet injection and ELM mitigation with the new active in-vessel saddle coils in ASDEX Upgrade

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